feat(i18n): draft of i18n with embedded TOML files

Supports rfc4646 language tags in env vars.
If region is detected (en-US, fr-CA), will try to load regional files first.

cobra.go

@@ -232,7 +232,7 @@ func stringInSlice(a string, list []string) bool {
 // CheckErr prints the msg with the prefix 'Error:' and exits with error code 1. If the msg is nil, it does nothing.
 func CheckErr(msg interface{}) {
 	if msg != nil {
-		fmt.Fprintln(os.Stderr, "Error:", msg)
+		fmt.Fprintln(os.Stderr, i18nError()+":", msg)
 		os.Exit(1)
 	}
 }

flag_groups.go

@@ -201,7 +201,7 @@ func validateExclusiveFlagGroups(data map[string]map[string]bool) error {
 
 		// Sort values, so they can be tested/scripted against consistently.
 		sort.Strings(set)
-		return fmt.Errorf("if any flags in the group [%v] are set none of the others can be; %v were all set", flagList, set)
+		return fmt.Errorf(i18nExclusiveFlagsValidationError(), flagList, set)
 	}
 	return nil
 }

go.mod

@@ -1,10 +1,12 @@
 module github.com/spf13/cobra
 
-go 1.15
+go 1.16
 
 require (
+	github.com/BurntSushi/toml v1.0.0
 	github.com/cpuguy83/go-md2man/v2 v2.0.3
 	github.com/inconshreveable/mousetrap v1.1.0
+	github.com/nicksnyder/go-i18n/v2 v2.2.1
 	github.com/spf13/pflag v1.0.5
 	gopkg.in/yaml.v3 v3.0.1
 )

localizer.go

@@ -0,0 +1,94 @@
+package cobra
+
+import (
+	"embed"
+	"fmt"
+	"github.com/BurntSushi/toml"
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+	"golang.org/x/text/language"
+	"os"
+)
+
+var defaultLanguage = language.English
+
+// envVariablesHoldingLocale is sorted by decreasing priority
+// These environment variables are expected to hold a parsable locale (fr_FR, es, en-US, …)
+var envVariablesHoldingLocale = []string{
+	"LANGUAGE",
+	"LC_ALL",
+	"LANG",
+}
+
+// localeFS points to an embedded filesystem of TOML translation files
+//
+//go:embed translations/*.toml
+var localeFS embed.FS
+
+// Localizer can be used to fetch localized messages
+var localizer *i18n.Localizer
+
+func i18nError() string {
+	return localizeMessage(&i18n.Message{
+		ID:          "Error",
+		Description: "prefix of error messages",
+		Other:       "Error",
+	})
+}
+
+func i18nExclusiveFlagsValidationError() string {
+	return localizeMessage(&i18n.Message{
+		ID:          "ExclusiveFlagsValidationError",
+		Description: "error shown when multiple exclusive flags are provided (group flags, offending flags)",
+		Other:       "if any flags in the group [%v] are set none of the others can be; %v were all set",
+	})
+}
+
+// … lots more translations here
+
+func localizeMessage(message *i18n.Message) string {
+	localizedValue, err := localizer.Localize(&i18n.LocalizeConfig{
+		DefaultMessage: message,
+	})
+	if err != nil {
+		return message.Other
+	}
+
+	return localizedValue
+}
+
+func loadTranslationFiles(bundle *i18n.Bundle, langs []string) {
+	for _, lang := range langs {
+		_, _ = bundle.LoadMessageFileFS(localeFS, fmt.Sprintf("translations/main.%s.toml", lang))
+	}
+}
+
+func detectLangs() []string {
+	var detectedLangs []string
+	for _, envKey := range envVariablesHoldingLocale {
+		lang := os.Getenv(envKey)
+		if lang != "" {
+			detectedLang := language.Make(lang)
+			appendLang(&detectedLangs, detectedLang)
+		}
+	}
+	appendLang(&detectedLangs, defaultLanguage)
+
+	return detectedLangs
+}
+
+func appendLang(langs *[]string, lang language.Tag) {
+	langString := lang.String()
+	langBase, _ := lang.Base()
+	*langs = append(*langs, langString)
+	*langs = append(*langs, langBase.ISO3())
+	*langs = append(*langs, langBase.String())
+}
+
+func init() {
+	bundle := i18n.NewBundle(defaultLanguage)
+	bundle.RegisterUnmarshalFunc("toml", toml.Unmarshal)
+	detectedLangs := detectLangs()
+	//fmt.Println("Detected languages", detectedLangs)
+	loadTranslationFiles(bundle, detectedLangs)
+	localizer = i18n.NewLocalizer(bundle, detectedLangs...)
+}

translations/main.en.toml

@@ -0,0 +1,7 @@
+[Error]
+description = "prefix of error messages"
+other = "Error"
+
+[ExclusiveFlagsValidationError]
+description = "error shown when multiple exclusive flags are provided (group flags, offending flags)"
+other = "if any flags in the group [%v] are set none of the others can be; %v were all set"

translations/main.fr.toml

@@ -0,0 +1,7 @@
+[Error]
+description = "prefix of error messages"
+other = "Erreur"
+
+[ExclusiveFlagsValidationError]
+description = "error shown when multiple exclusive flags are provided (group flags, offending flags)"
+other = "les options [%v] sont exclusives, mais les options %v ont été fournies"